1. Field of the Invention
The invention relates to a contact tip for a welding electrode. Such contact tips are generally used in welding devices as for example in arc welding torches. Contact tips of this kind constitute contact devices for the transfer of the welding current to the welding electrode, for example a solid wire electrode or a tubular electrode with a powder filling, as it is fed through the contact tip.
2. Description of the Prior Art
Prior art contact tips have the form of a tube, the internal diameter of which is slightly larger than the diameter of the electrode. The electrode slides during its passage through the contact tip tube against the inner wall of the tube thereby establishing the desired contact for the transfer of current from the contact tip tube to the welding electrode. Known are certain types of contact tip tubes which are slightly curved in one plane thereby improving the contact between the electrode and the tube. As a general rule, the position of the contact area of the electrode and the contact tip is not fixed. The length of the electrode between the tip of the electrode and this contact area which is passed by the welding current, varies. As a consequence, the energy supply to the welding pool fluctuates, which adversely affects the welding quality. Prior art contact tip tubes pose another problem because of surface impurities and coatings on electrodes.
There is described in the U.S. Pat. No. 3,112,393 a tubular contact nozzle with a helix-shaped passage for the electrode. Continuous electrical contact between the electrode and the inner wall of the nozzle is established throughout the length of the nozzle. The manufacture of this nozzle, which starts from a tube with small bore, is quite complicated and therefore costly.
Electrodes are often treated with a protective coating to prevent oxidation and deterioration. Morevoer, the surface of the electrode may become contaminated with dust and other deterious substances as for example abrased material from the electrode guides. These materials may constrict the narrow bore of a tubular contact nozzle and prohibit a uniform advancement of the electrode.
The contact nozzle should be an inexpensive item as it is worn out very quickly. Its service life is generally reckoned in hours.